Heretofore, a fuel cell system, which includes a fuel cell for receiving a supplied reactant gas (a fuel gas and an oxidizing gas) to generate a power, has been suggested and put to practical use. Such a fuel cell system is provided with a pipe forming a fuel supply passage through which the fuel gas supplied from a fuel supply source such as a hydrogen tank flows to the fuel cell. Moreover, this pipe (the fuel supply passage) is usually provided with a pressure regulation valve (a regulator) which reduces the supply pressure of the fuel gas from the fuel supply source to a constant value.
Moreover, at present, a technology has been suggested in which an on/off valve for changing the supply state (a supply amount, a supply pressure or the like) of the fuel gas is provided in the pipe (the fuel supply passage) to change the supply state of the fuel gas in accordance with the operation state of the system (e.g., see Japanese Patent Application Laid-Open No. 2005-302563).